(a) Field
The subject matter disclosed generally relates to tow vehicles or to wreckers. More particularly, the subject matter disclosed relates to drag winch assemblies for tow vehicles which include slidable boom assemblies and to methods of operating the same.
(b) Related Prior Art
Nowadays, a traditional tow vehicle or wrecker for heavy loads generally has two functions. The first one is to lift a wrecked object with an underlift, to ensure it is fixed to the underlift and then to move such wrecked object out of a traffic artery or area. The second one is to hang a wrecked object from a boom assembly and to transfer it to a new site suitable for successive operations (i.e., lift the wrecked object with the under lift, fix the wrecked object and the like).
As shown in prior art FIGS. 1 and 2, a conventional tow vehicle or wrecker 10 for heavy loads may include a main frame 12 and a boom assembly 14 which has a first end (bottom end) 16 and a second end (top end) 18. The boom assembly 14 is either fixed, i.e. unable to rotate, or pivotably mounted at its first end 16 to the main frame 12 of the wrecker 10 such as to allow the second end 18 of the boom assembly 14 to displace, at least up and down (and optionally left and right), relative to the first end 16. Accordingly, the boom assembly 14, which defines a boom longitudinal axis 20, may pivot between a horizontal position, where the boom longitudinal axis 20 is substantially parallel to a ground surface, and a vertical position, where the boom longitudinal axis is substantially perpendicular to the ground surface.
At its second end 18, or about its second end 18, the boom assembly 14 further includes a pulley assembly 22 which is rotatably mounted about a pulley axis 24 for receiving a lifting cable 26. The boom assembly 14 further includes a winch assembly 28 which is to be coupled to a motor (not shown) for driving the winch assembly 28. Wound upon the winch assembly 28 is the lifting cable 26. The lifting cable 26 extends from the winch assembly 28 towards the pulley assembly 22 which receives the lifting cable 26. The lifting cable 26 usually includes one or more hooks 30 for lifting the wrecked object 32, when at an important distance of the main frame 12 of the wrecker 10.
There exists in the industry wreckers, such as wreckers 10, where the winch assembly 28 includes four winch assemblies and where the pulley assembly 22 includes four corresponding pulley assemblies for receiving the corresponding cables. Two of the winch/pulley assemblies may be considered to be the main winch/pulley assemblies while the two others may be considered to be the secondary winch/pulley assemblies. Such winch/pulley assemblies may be used by the operator of the wrecker 10 mainly to lift the wrecked object 32.
As shown in prior art FIGS. 1 and 2, there also exists in the industry boom assemblies 14 that are slidably mounted on main frames 12 of a wrecker 10 that is slidable between a frontmost position (prior art FIG. 1) and a rearmost position (prior art FIG. 2). Designed for most difficult operations, these slidable boom assemblies 14 bring the operator an improved usable boom assembly capacity. Such slidable boom assemblies 14 thus increase the working area of the operator of the wrecker 10 and provide him with a maximum boom lifting capacity in unusual boom working areas (prior art FIG. 3). Such a slidable boom assembly 14 may also prevent the wrecker 10 from adopting an unstable position during lifting operations.
In addition to the slidable boom assembly 14 providing the operator with one, two, three or four lifting cables 26 (via the slidable boom assembly 14) for lifting operations, some wreckers 10 that include the slidable boom assembly 14 (or that do not include it) further include a dragging cable wounded to a drag winch assembly for dragging operations.
However, such drag winch assemblies are usually mounted on a rear portion of a main frame of a wrecker. As shown in prior art FIGS. 4 and 5, a drag winch assembly 34 is mounted on a rear portion 36 of a main frame 12 of a wrecker 10. According to prior art FIGS. 4 and 5, the drag winch assembly 34 is mounted on an underlift structure 38 of the wrecker 10. Drag winch assemblies found in the industry are not configured to be mounted on a main frame of a wrecker 10 that includes a slidable boom assembly as conventional drag winch assemblies are voluminous. These drag winch assemblies generate an important weight about the rear portion of the main frame of the wrecker. Since the towing capacity of the wrecker is decreased as the load is increased above the axle of the wrecker, such a configuration is thus not recommended. Additionally, with this prior art configuration of the drag winch assembly being fixedly mounted at the rear portion of the main frame, the slidable boom assembly is not allowed to be displaced completely from its frontmost position to its rearmost position in view of the load bearing capacity of the wrecker 10 (prior art FIGS. 1 and 2).
Referring now to prior art FIG. 6, there is shown another drag winch assembly 34 mounted about a rear portion 36 of a main frame 12 of a wrecker 10. The drawbacks discussed above may also be applied to this wrecker configuration.
There is therefore a need for a drag winch assembly for a tow vehicle that includes a slidable boom assembly and for a method of operating a drag winch assembly of a tow vehicle that includes a slidable boom assembly.